Maintaining a large legacy software system is notoriously difficult. Such systems can be critical to continued operation of a business, but they are often pieced together by scores of different programmers over a period of years. The result is a system with millions of lines of code and little relevant documentation. The original developers often move on to other projects, and waves of successors have edited, extended, and enhanced the software system using a variety of technologies and techniques.
All software must evolve over time to meet change, and legacy systems are no exception. However, a seemingly simple change to a legacy software system can become a monumental effort. Even if a top-notch programming team is put to task, it can take an enormous effort to decipher the structure and operation of the system.
Software development environments do offer tools for helping a programming team deal with a legacy system. For example, searching mechanisms can be employed to find every occurrence of a keyword in the source code. So, if a change is going to be made, the full impact can be investigated. Careful searching can reveal much about how the software operates. However, simple keyword searching, even in the hands of an expert, has severe limitations. In many cases, too few or too many keyword hits are found, limiting the usefulness of current search tools. So, improvements to the tools are sorely needed.